Hundreds of pilot whales have become beached in the shallow waters of Macquarie Harbour, on the west coast of Tasmania. Many of the whales are dead, the BBC reports.
The stranding event is the largest ever recorded in Tasmania, Kris Carlyon, a wildlife biologist with the Australian state’s Marine and Conservation Program, said in a Department of Primary Industries, Parks, Water and Environment statement today (September 23). Carlyon is part of the effort to rescue the living whales from the sand bars of the harbor and return them to deeper waters.
“Pilot whales are deep-water species that are not accustomed to shallow waters or tides and may not be able to navigate well using their biosonar in shallow and sandy environments,” Fleur Visser, the scientific director of Kelp Marine Research, writes in an email to The Scientist.
Annebelle Kok, a marine biologist at the University of California, San Diego, and a collaborator of Visser on a recent pilot whale study, tells The Scientist it might be the animal’s strong social bonds that led to such a mass stranding. It’s possible that “as one animal swims towards the coast, the rest will follow, leading to the whole group stranding at once,” she writes in an email. Because of their social nature, she says, the number of pilot whales that stranded is not surprising.
Pilot whales are a common species suffering mass strandings, but the recent event is historic in Tasmania. In 1935, close to 300 long-finned pilot whales stranded near Stanley, by the northern tip of the Australian island state, and in 1998, 216 stranded near Marion Bay on the east side of the island.
Both Kok and Visser say that what has caused the whales to strand is uncertain. “In this case, one of the possibilities is that certain anomalies or oceanographical features, or perhaps illness, have interfered with pilot whale navigation, leading them into shallow water from which they cannot easily escape,” Visser writes. Variations in the architecture of the seafloor can lead to the whales swimming toward shore, rather than away from it, Kok explains. “This is for example a hypothesis for why so many whales strand in New Zealand.”
Human sounds, such as the use of sonar, should also be considered, the scientists say. Visser notes mass strandings have been recorded “before the advent of wide-spread man made noise in the ocean,” so sound may not be the cause of the stranding. Still, she says, “we do need to investigate possible causes, through investigation of the health and possible injuries of the stranded animals,” and also by creating a list of human activities in the possible areas the whales visited in the days before the stranding began.
“Unfortunately, there are still many instances in which we don’t know why the whales stranded,” Kok says.
As rescue teams work to identify possible causes of the mass stranding and move the live whales away from shallow waters, authorities have begun to consider what to do with the dead whales scattered along the coast. In the past, whales have been towed out to sea or buried ashore, according to the BBC.
“We have a couple of options that we are considering, but we need to consider all aspects before we settle on a decision,” Nic Deka, Incident Controller and Parks and Wildlife Service regional manager, says in the Department of Primary Industries, Parks, Water and Environment statement. “We can’t leave the whales in the harbour as they will present a range of issues. We are committed to retrieving and disposing but our key priority is to remain focussed on the rescue effort.”
“Any whale we save we are considering a real win,” Carlyon said in a statement issued Tuesday (September 22). “We are focusing on having as many survivors as we can.”